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| author | Fangyi Zhou <fangyi.zhou15@imperial.ac.uk> | 2018-10-28 12:28:53 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2018-10-28 13:40:14 -0400 |
| commit | 8e1a5593f940b9d2882a5e81abf028e7b99aff3a (patch) | |
| tree | bf3a4b4c5f1855e8ed8e8aa27b80293164eaa480 /testsuite/tests/numeric | |
| parent | c4a876d5f99554e87400946dd26ca11819d11673 (diff) | |
| download | haskell-8e1a5593f940b9d2882a5e81abf028e7b99aff3a.tar.gz | |
Fix integer overflow when encoding doubles (Trac #15271)
Summary:
Ticket #15271 reports a case where 1e1000000000 is incorrectly
converted to 0.0. After some investigation, I discovered the number is
converted to rational correctly, but converting the ratio into a double
introduced an error.
Tracking down to how the conversion is done, I found the rts float
implementation uses `ldexp`, whose signature is
`double ldexp (double x, int exp);`
The callsite passes an `I_` to the second argument, which is
platform-dependent. On machines where `I_` is 64 bits and `int` is 32 bits, we
observe integer overflow behaviour.
Here is a mapping from rational to exponent with observations
1e646457008 -> 2147483645 (result = infinity, positive in int32)
1e646457009 -> 2147483648 (result = 0.0, overflow to negative in int32)
1e1000000000 -> 3321928042 (result = infinity, overflow to positive in int32)
1e1555550000 -> 5167425196 (result = 0.0, overflow to negative in int32)
We fix this issue by comparing STG_INT_MIN/MAX and INT_MIN/MAX and bound the
value appropriately.
Test Plan: New test cases
Reviewers: bgamari, erikd, simonmar
Reviewed By: bgamari
Subscribers: rwbarton, carter
GHC Trac Issues: #15271
Differential Revision: https://phabricator.haskell.org/D5271
Diffstat (limited to 'testsuite/tests/numeric')
| -rw-r--r-- | testsuite/tests/numeric/should_run/T15271.hs | 5 | ||||
| -rw-r--r-- | testsuite/tests/numeric/should_run/T15271.stdout | 4 |
2 files changed, 9 insertions, 0 deletions
diff --git a/testsuite/tests/numeric/should_run/T15271.hs b/testsuite/tests/numeric/should_run/T15271.hs new file mode 100644 index 0000000000..c8f2c95de5 --- /dev/null +++ b/testsuite/tests/numeric/should_run/T15271.hs @@ -0,0 +1,5 @@ +main = do + print 1e646457008 + print 1e646457009 -- T15271: This incorrectly printed 0.0 + print 1e1555550000 -- This is still infinity + print 1e1000000000 -- T15271: This incorrectly printed 0.0 diff --git a/testsuite/tests/numeric/should_run/T15271.stdout b/testsuite/tests/numeric/should_run/T15271.stdout new file mode 100644 index 0000000000..6e89f246c1 --- /dev/null +++ b/testsuite/tests/numeric/should_run/T15271.stdout @@ -0,0 +1,4 @@ +Infinity +Infinity +Infinity +Infinity |